THE Greens leader, Senator Christine Milne, has endorsed a controversial hoax by an anti-coal activist, saying his actions were ''part of a long and proud history of civil disobedience, potentially breaking the law, to highlight something wrong''.

THE Greens leader, Senator Christine Milne, has endorsed a controversial hoax by an anti-coal activist, saying his actions were ''part of a long and proud history of civil disobedience, potentially breaking the law, to highlight something wrong''.

Her comments came after a tweet by her colleague Lee Rhiannon, who publicly congratulated Jonathan Moylan, an activist under scrutiny for impersonating a bank and temporarily wiping $314 million off the value of Whitehaven Coal.

Mr Moylan orchestrated an elaborate hoax on Monday in which he tricked investors into thinking that a recent $1.2 billion loan arranged by ANZ for Whitehaven had been cancelled on ethical grounds.

Shares in Whitehaven, which counts the struggling coal baron Nathan Tinkler as its biggest shareholder, fell from $3.52 to $3.21 in rapid time before the stock was put into a trading halt.

Mr Moylan designed a fake ANZ press template, website and dummy email inbox online and impersonated a company spokesperson to callers, including Fairfax Media. Moylan is now obtaining legal representation, and has received calls from ASIC.

Senator Milne's statement and Senator Rhiannon's tweet come as the Greens try to appeal to new constituencies and recast themselves as less ''extreme'' in an election year.

Last month, the party revealed a new platform of policies aimed at presenting a smaller target.

Senator Rhiannon's tweet has raised eyebrows on the social media site and exposed her to ridicule.

Brisbane tweeter Cameron Lloyd asked Senator Rhiannon: ''What about mum & dad investors that lost money? Their fault for investing in coal?'' Simon Black, also from Brisbane, said: ''I know greens can be a bit out there but openly endorsing breaking the law is breathtakingly odd.''

But Senator Milne expanded upon her colleague's comment.

''The two hottest days in Australian history have just been recorded and fires are burning around the country,'' she said.

''Companies that are driving climate change will increasingly come under scrutiny and be exposed for their investments and actions, and Jonathan Moylan is drawing attention to these companies. As with asbestos and tobacco, coal is going to come under increasing pressure''.

The Greens communications director, Tim Hollo, also defended Senator Rhiannon, replying to one of her critics on Twitter: ''On the day @BobBrownFndn took on the leadership of Sea Shepherd, it's weird to attack @leerhiannon for defending the hoax''.

Mr Hollo was referring to the announcement that former Australian Greens leader Bob Brown is to take over running the Antarctic anti-whaling campaign by the hardline conservationists Sea Shepherd.